I have found a way to use grub to boot from usb (avoids all detection issues at boot). This howto works specifically for xubuntu 8.10, but you can apply the same process for Ubuntu and Kubuntu.
This is thanks to the USBCDX810.iso from www.pendrivelinux.com, which is designed to create a bootable cd-rom when your PC cannot / will not boot directly from a usb flash drive. Here's how you do it. (Howto probably not for Newbies )
Download the USBCDX810.iso from here: http://downloads.sourceforge.net/pen.../USBCDX810.iso (only @ 10mb)Requirements: A PC with some kind of Linux installed with grub as the bootloader. If you have a Windows install and want to acheive the same thing, see TJCIB's post further down. I did this using my Xubuntu 8.10 hard drive installation, you may need to modify paths if your distro / grub puts things / requires things in a different place.
Using gmountiso or similar iso mounting program mount the iso
Create a new folder in your /boot directory, I used /boot/usb-boot
Copy the grub folder, vmlinuz and initrd.gz files across from the mounted iso to your new directoryCode:sudo mkdir /boot/usb-boot
where /media/iso is the location of your mounted isoCode:cp -R /media/iso/boot/* /boot/usb-boot
Next open up your grub menu.lst:
Add the following to the bottom:Code:sudo nano /boot/grub/menu.lst
This assumes your system is running on the first partition of the first hard drive. Substitute (hd0,0) for the correct path. You can edit out quiet and splash if you like to watch what is going on, and remove the persistent entry if you are not running a persistent flash drive.title Run Xubuntu 8.10 from USB FLASH DRIVE
kernel /boot/usb-boot/vmlinuz file=/cdrom/preseed/xubuntu.seed boot=casper noprompt cdrom-detect/try-usb=true persistent quiet splash
Save out, unmount the iso and reboot, inserting your flash drive as you go.
You may want to edit your bios settings to stop your PC directly booting from the flash drive. (Yes, this sounds odd, mine does, but I wanted a way of doing this from grub, so I stopped the bios from doing it)
On reboot, press ESC if you need to show your grub menu, then select the Run "Xubuntu 8.10 from USB FLASH DRIVE" entry at the bottom, and with any luck, you should start booting up from your USB Flash Drive.
A bit more work, but a more elegant solution in my opinion.
pendrivelinux also has similar boot isos for Ubuntu and Kubuntu, and you can edit the menu.lst lines to your own preference.
See also zasf's post about the DIY approach for a boot CD
Although the link for the boot cd is still up, pendrive linux have changed things a biyt and now tell you how to create a boot cd rather than providing one.
For xubuntu 8.10 go here: http://www.pendrivelinux.com/usb-boo...r-xubuntu-810/
They don't appear to have moved up to 9.04 yet